Transistor-based zinc sensor

ABSTRACT

Embodiments of the invention are directed to a solid-state zinc sensor. A non-limiting example of the sensor includes a semiconductor substrate. The sensor can also include an assembly surface on the semiconductor substrate. The sensor can also include a zinc detection monolayer chemically bound to the assembly surface. The sensor can also include a power supply electrically connected to the semiconductor substrate.

BACKGROUND

The present invention generally relates to fabrication methods andresulting structures for semiconductor devices. More specifically, thepresent invention relates to transistor-based (e.g., field effecttransmitter (FET)-based) zinc sensors.

Zinc can play an important role in biological systems. In healthyindividuals, zinc homeostasis is established and maintained for propercellular functions. Disruptions or fluctuations in zinc levels inbiological systems, however, can be correlated with a variety ofneurological diseases and disorders. For instance, aberrantconcentrations of zinc ions can be associated with Alzheimer's disease,amyotrophic lateral sclerosis (ALS), Parkinson's disease, ischemia, andepilepsy. Measuring and monitoring cellular zinc concentrations inbiological systems can be useful in the treatment and study of suchdiseases and disorders.

SUMMARY

Embodiments of the invention are directed to a transistor-based zincsensor. A non-limiting example of the sensor includes a semiconductorsubstrate. The sensor can also include an assembly surface on thesemiconductor substrate. The sensor can also include a zinc detectionmonolayer chemically bound to the assembly surface. The sensor can alsoinclude a power supply electrically connected to the semiconductorsubstrate.

Embodiments of the present invention are directed to a method forfabricating a solid-state zinc sensor. A non-limiting example of themethod includes forming an assembly surface on a semiconductor substrateof a semiconductor system. The method can also include attaching a zincdetection monolayer to the assembly surface. The method can also includeconnecting a power supply to the semiconductor system. The method canalso include connecting a current detector to the assembly surface.

Embodiments of the present invention are directed to a method ofoperating a solid-state zinc sensor. A non-limiting example of operatingthe method includes attaching a zinc detection monolayer to an assemblysurface of a semiconductor system, wherein the semiconductor systemincludes a source, a drain, and a gate. The method can also includeapplying a source-drain bias to the semiconductor system. The method canalso include measuring a first drain current. The method can alsoinclude exposing the zinc detection monolayer to a biological fluid. Themethod can also include measuring a second drain current. The method canalso include determining a zinc concentration of biological fluid basedat least in part upon the first drain current and the second draincurrent.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 depicts a zinc sensor system according to embodiments of theinvention;

FIG. 2A depicts a cross-sectional side view of a zinc sensor after afabrication operation according to embodiments of the invention;

FIG. 2B depicts a top-down view of a zinc sensor after a fabricationoperation according to embodiments of the invention;

FIG. 2C depicts a cross-sectional side view of a zinc sensor afteranother fabrication operation according to embodiments of the invention;

FIG. 3 depicts a flow diagram illustrating a method according to one ormore embodiments of the invention; and

FIG. 4 depicts a flow diagram illustrating a method according to one ormore embodiments of the invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedescribed embodiments of the invention, the various elements illustratedin the figures are provided with two or three digit reference numbers.With minor exceptions, the leftmost digit(s) of each reference numbercorrespond to the figure in which its element is first illustrated.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor device and integrated circuit (IC) fabrication may or maynot be described in detail herein. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor devices andsemiconductor-based ICs are well known and so, in the interest ofbrevity, many conventional steps will only be mentioned briefly hereinor will be omitted entirely without providing the well-known processdetails.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, zinc is an important mineral for avariety of biological functions and is present in high levels in thebrain. Zinc homeostasis includes maintaining a constant biological stateof zinc. The homeostasis of free zinc ions, and related impairments,have been directly linked to a variety of neurological diseases andconditions, such as Alzheimer's, ALS, Parkinson's disease, ischemia, andepilepsy. Investigation of zinc homeostasis, therefore, can be acritical component of research and treatment of such conditions.

Conventional measurement of zinc ions using optical methods can requirecumbersome equipment or off-site measurement. The ability to provideon-site, sensitive results in studies of zinc concentration andconcentration changes is desirable in biological applications, which caninvolve relatively small changes in concentration over a short period oftime.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention provide a solid state, transistor-basednon-optical zinc sensor for determination of zinc concentration inbiological fluids. Embodiments of the present invention include aFET-based sensor with a functionalized surface capable of binding zincions. Upon binding zinc ions, sensors according to embodiments of theinvention can experience a change in electrical output relative to theelectrical output of a surface free of zinc ions directly proportionalto bound ion concentration.

The above-described aspects of the invention can allow sensitive,on-site measurement of zinc concentrations in biological fluid foranalysis, study, and treatment of neurological conditions implicatingzinc homeostasis by providing a portable, transistor-based zinc sensorthat is light weight and cost effective. Embodiments of the inventioncan provide sensitive zinc measurements without the need for heavy orspecialized equipment by using a transistor-based system that does notrequire optical components for ionic detection. Embodiments of theinvention can leverage changes in electrical properties of atransistor-based system upon binding of a positively charged zinc ion todetermine zinc concentrations in biological fluid.

Turning now to a more detailed description of aspects of the presentinvention, FIG. 1 depicts a cross-sectional side view of an exemplarytransistor-based zinc sensor 100 according to embodiments of theinvention. The sensor 100 can include an assembly surface 104 and asemiconductor substrate 102. The substrate 102 can be a substrate of afield effect transistor. The sensor 100 can also include a zincdetection monolayer 106. The zinc detection monolayer 106 can bechemically bound to the assembly surface 104. In some embodiments of theinvention, the zinc detection monolayer 106 is chemically selective tozinc ions. The sensor 100 can also include a power supply 110electrically connected to the system 100, for example to thesemiconductor substrate. In some embodiments of the invention, a powersupply 110 is electrically connected to a source and drain of aFET-based transistor. In some embodiments of the invention, the system100 includes a current detector or voltage detector 112. In operation,the system 100 can be placed in contact with a biological fluid 110. Thebiological fluid 110 can include zinc ions (Zn²⁺) 108.

In some embodiments of the invention, the semiconductor substrate 102includes silicon. In some embodiments of the invention, thesemiconductor substrate includes a semiconductor on insulator (SOI)wafer. An SOI wafer can include a thin layer of a semiconductingmaterial atop an insulating layer (e.g., an oxide layer) which is inturn disposed on a silicon substrate. The semiconducting material caninclude, but is not limited to, Si (silicon), strained Si, SiC (siliconcarbide), Ge (geranium), SiGe (silicon germanium), SiGeC(silicon-germanium-carbon), Si alloys, Ge alloys, GaAs (galliumarsenide), InAs (indium arsenide), InP (indium phosphide), or anycombination thereof. In some embodiments of the invention, thesemiconductor substrate 102 includes carbon nanotubes, such as a thinlayer of carbon nanotubes atop a silicon substrate or atop an insulatinglayer of an SOI wafer. In some embodiments of the invention, thesemiconductor substrate 102 includes silicon or carbon nanotubes aschannel material.

Assembly surface 104 can include, for example, a dielectric layer of aFET-based transistor. In some embodiments of the invention, assemblysurface 104 includes an oxide layer, such as silicon dioxide,tetraethylorthosilicate (TEOS) oxide, high aspect ratio plasma (HARP)oxide, high temperature oxide (HTO), high density plasma (HDP) oxide,oxides (e.g., silicon oxides) formed by an atomic layer deposition (ALD)process, or any combination thereof. In some embodiments of theinvention, assembly surface 104 includes a metal oxide, such as an oxideof hafnium (Hf), aluminum (Al), tungsten (W), or titanium (Ti). In someembodiments of the invention, the assembly surface 104 includes silicondioxide (SiO₂) or a silicon group such as bare silicon with Si—H bondson the surface for functionalization or for example amorphoushydrogenated silicon (Si—H).

Zinc detection monolayer 106 can form a sensing surface of the system100. The zinc detection monolayer 106 can include, for example, amonolayer selectively formed on metal oxides, such as HfO₂ or Al₂O₃ ofan assembly surface 104. In some embodiments of the invention, zincdetection monolayer 106 includes a compound capable of binding zincions, such as di-picolylamine or derivatives thereof. Di-picolylamine,for example, is known to bind to free zinc ions and can be attached toan assembly surface 104, for example, through a hydroxamic acid group.In operation, when zinc ions bind to the zinc detection monolayer 106,the electrical properties, such as a system current, can change, forinstance due to the association of added positive charge to the systemfrom the zinc ions.

The zinc detection monolayer 106 can be self-assembled onto the assemblysurface 104 of a standard FET device, for instance, after cleaning theassembly surface 104. The modified surface can be placed in a solutioncontaining free zinc ions, such as a biological fluid, and electricaldata can be recorded before and after adding zinc ions. In someembodiments of the invention, the biological fluid is brain fluid.Complexation of zinc ion with picolylamine can change the surface chargeof the assembly surface 104 and can result in a change in electricaloutput that is directly proportional to the concentration of free zincions.

In some embodiments of the invention, the zinc detection monolayerincludes a compound of the following formula:

wherein N is nitrogen and R includes an acid, an ether, an alcohol, analkene, an alkane, or a silicon group.

FIGS. 2A-2C depict a schematic illustrating an exemplary method offabricating a solid-state zinc sensor according to one or moreembodiments of the present invention. FIG. 2A illustrates across-sectional side view of an exemplary semiconductor substrate 102including an assembly surface 104 according to one or more embodimentsof the present invention. The assembly surface, for example, can be, forexample, a nanowire deposited on the surface of the semiconductorsubstrate. FIG. 2B illustrates a top-down view of the exemplarysemiconductor substrate 102 and assembly surface 104 shown in FIG. 2A.

As is illustrated in FIG. 2C, the assembly surface 104 can befunctionalized with a zinc detection monolayer 106. In some embodimentsof the invention, when the assembly surface 104 includes a metal-oxidesurface, a zinc detection monolayer can be formed from a reactionbetween the surface with a compound of formula (I)

wherein N is nitrogen and R is —CONHOH or PO₃H. In some embodiments ofthe invention, when the assembly surface 104 includes a silicon dioxidesurface, a zinc detection monolayer can be formed from a reactionbetween the surface with a compound of formula (I) above, wherein R is—Si(O(CH₂CH₃)₂, SiCl(OCH₂CH₃), or SiCl₃. In such embodiments of theinvention, for example, the zinc detection monolayer can be prepared inone step starting from a compound in which R is Cl using a metal halogenexchange according to methods known to those skilled in the art. In someembodiments of the invention, when the assembly surface 104 includes asurface including bare silicon with Si—H bonds on the surface, a zincdetection monolayer can be formed from a reaction between the surfacewith a compound of formula (I) above, wherein R is —C═C, —OH, or CCH.

FIG. 3 depicts a flow diagram of an exemplary method 300 of fabricatinga solid-state zinc sensor according to one or more embodiments of thepresent invention. The method 300 can include, as shown at block 302,forming an assembly surface on a semiconductor substrate of a FET-basedsystem. The FET-based system can include a semiconductor systemincluding a source, drain, and gate, for example. The method 300 canalso include, as shown at block 304, attaching a zinc detectionmonolayer to the assembly surface. The method 300 can also include, asshown at block 306, connecting a power supply to the FET-based system.The method 300 can also include, as shown at block 308, connecting acurrent detector to the assembly surface.

FIG. 4 depicts a flow diagram of an exemplary method 400 of operating asolid-state zinc sensor according to one or more embodiments of thepresent invention. The method 400 can include, as shown at block 402,attaching a zinc detection monolayer to an assembly surface of asemiconductor system, wherein the semiconductor system includes asource, a drain, and a gate. The method 400 can also include, as shownat block 404, applying a source-drain bias to the semiconductor system.The method 400 can also include, as shown at block 406, measuring afirst drain current. The first drain current, for instance, can includea drain current when a source-drain bias is applied before exposure to afluid containing zinc. The method 400 can also include, as shown atblock 408, exposing the zinc detection monolayer to a fluid, such as abiological fluid. The method 400 can also include, as shown at block410, measuring a second drain current. The second drain current, forinstance, can include a drain current when a source drain bias isapplied after or during exposure to the biological fluid. The method 400can also include, as shown at block 412, determining a zincconcentration of biological fluid based at least in part upon the firstdrain current and the second drain current.

In some embodiments of the invention, changes in output current caneasily detect zinc ions in biological solutions. Desirably, zinc ionconcentrations can conveniently be measured on-site without the need foroptical systems or specialized or heavy equipment.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to semiconductor device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the semiconductordevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device. Semiconductor lithography is the formation ofthree-dimensional relief images or patterns on the semiconductorsubstrate for subsequent transfer of the pattern to the substrate. Insemiconductor lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures that makeup a transistor and the many wires that connect the millions oftransistors of a circuit, lithography and etch pattern transfer stepsare repeated multiple times. Each pattern being printed on the wafer isaligned to the previously formed patterns and slowly the conductors,insulators and selectively doped regions are built up to form the finaldevice.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments of the invention, the practicalapplication or technical improvement over technologies found in themarketplace, or to enable others of ordinary skill in the art tounderstand the embodiments described herein.

What is claimed is:
 1. A solid-state zinc sensor comprising: asemiconductor substrate; an assembly surface on the semiconductorsubstrate; a zinc detection monolayer chemically bound to the assemblysurface, wherein the zinc detection monolayer is more chemicallyselective to zinc ions than to non-zinc ions and non-ions; and a powersupply electrically connected to the semiconductor substrate. 2.(canceled)
 3. The sensor of claim 1, wherein the semiconductor substratecomprises carbon nanotubes.
 4. The sensor of claim 1, wherein thesemiconductor substrate comprises silicon.
 5. The sensor of claim 1,wherein the assembly surface comprises a metal oxide layer.
 6. Thesensor of claim 5, wherein the metal oxide layer comprises hafniumoxide, aluminum oxide, tungsten oxide, or titanium oxide.
 7. The sensorof claim 1, wherein the zinc detection monolayer comprises a compound offormula:

wherein N is nitrogen and R comprises an acid, an ether, an alcohol, analkene, an alkane, or a silicon group. 8.-20. (canceled)